Wireless power transferring devices, such as Inductively Coupled Power Transfer systems (ICPT), are used for transferring power from a power transferring unit to a power receiving unit. Wireless power transferring devices are for example used for charging battery units of an electric vehicle.
The power transferring unit is adapted to generate an alternating magnetic field of high frequency. The magnetic field couples the power transferring unit to the power receiving unit over a gap with a medium. The gap is often denoted “air gap” even if other medium than air is used in the gap.
The power receiving unit is adapted to be subjected to the alternating magnetic field and induce an alternating current. The induced alternating current is for example used to power a load or rectified and used for charging batteries.
A problem with wireless power transferring devices is that ferromagnetic materials, such as a steel body of a vehicle, in vicinity of the device is subjected to the alternating magnetic field, wherein the material is heated up due to eddy currents. Accordingly, the energy transfer efficiency between the power transferring unit and the power receiving unit is not optimal. Furthermore, it is important to limit the spread of the alternating magnetic field to the surrounding environment since high flux of the alternating magnetic field could have biological impact on people and animals.
US2009/0267558 discloses a wireless power charging system comprising a primary core and a secondary core. The primary core comprises a transmission shield panel. The secondary core comprises an eddy current reducing member and receiving shield panel.
WO2008/140333 discloses an inductive power transfer unit for charging electrical vehicles. The unit comprises a coil and a ferrite core, which ferrite core comprises a plurality of bars protruding away from a center of the unit. The outer part of the bars comprises insulating pads of foam or rubber adapted to protect the bars from mechanical stress caused by impacts and vibrations.